Personally, I don't think he cares about the issue in the sense that most do...he may have his personal opinion aboout it, but he supports the constitution and what it has to say about it...which is that the federal government has no stand. It is a matter that should be left to the states to decide.
States ratify Amendments to the Constitution...
READ it for yourself...
Article V
The Congress, whenever two thirds of both houses shall deem it necessary, shall propose amendments to this Constitution, or, on the application of the legislatures of two thirds of the several states, shall call a convention for proposing amendments, which, in either case, shall be valid to all intents and purposes, as part of this Constitution, when ratified by the legislatures of three fourths of the several states, or by conventions in three fourths thereof, as the one or the other mode of ratification may be proposed by the Congress;...